Method and apparatus for producing large, single-crystals of aluminum nitride

• US 8,123,859 B2
• Filed: 07/22/2010
• Issued: 02/28/2012
• Est. Priority Date: 12/24/2001
• Status: Expired due to Term

• Current Assignee: Crystal IS, Inc. (Asahi Kasei Corporation)
• Original Assignee: Crystal IS, Inc. (Asahi Kasei Corporation)
• Inventors: Schowalter, Leo J., Slack, Glen A., Rojo, J. Carlos
• Primary Examiner(s): Kunemund, Bob M
• Application Number:
  US12/841,350
• Publication Number:
  US 20110011332A1
• Time in Patent Office: 586 Days
• Field of Search: 117/89, 117/105, 117/108, 117/109, 117/942
• US Class Current: 117/89
• CPC Class Codes: C30B 11/003 Heating or cooling of the melt or the crystallised material
• CPC Class Codes: C30B 23/00 Single-crystal growth by condensing evaporated or sublimed materials
• CPC Class Codes: C30B 29/403 AIII-nitrides
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 33/0075 comprising nitride compounds
• CPC Class Codes: H01L 33/025 Physical imperfections, e.g. particular concentration or distribution of impurities

Abstract

A method and apparatus for producing bulk single crystals of AlN having low dislocation densities of about 10,000 cm⁻² or less includes a crystal growth enclosure with Al and N₂ source material therein, capable of forming bulk crystals. The apparatus maintains the N₂ partial pressure at greater than stoichiometric pressure relative to the Al within the crystal growth enclosure, while maintaining the total vapor pressure in the crystal growth enclosure at super-atmospheric pressure. At least one nucleation site is provided in the crystal growth enclosure, and provision is made for cooling the nucleation site relative to other locations in the crystal growth enclosure. The Al and N₂ vapor is then deposited to grow single crystalline low dislocation density AlN at the nucleation site. High efficiency ultraviolet light emitting diodes and ultraviolet laser diodes are fabricated on low defect density AlN substrates, which are cut from the low dislocation density AlN crystals. Bulk crystals of ZnO may also be produced using the method.

Claims

1. A method of producing single-crystal AlN in a predominantly N₂-filled environment, the method comprising:

providing Al and N₂ vapor in a crystal growth enclosure, the crystal growth enclosure comprising a selective barrier configured to substantially prevent passage of Al vapor and permit passage of N₂ vapor therethrough;

maintaining in the crystal growth enclosure, (i) an N₂ partial pressure greater than stoichiometric pressure relative to the Al, and (ii) a total vapor pressure at super-atmospheric pressure;

providing at least one nucleation site in the crystal growth enclosure;

cooling the nucleation site relative to other locations in the crystal growth enclosure;

generating a flow of N₂ vapor past the nucleation site; and

depositing the Al and N₂ vapor under conditions capable of growing single crystalline AlN originating at the nucleation site.

2. The method of claim 1, wherein cooling the nucleation site comprises disposing the crystal growth enclosure within a temperature gradient.

3. The method of claim 2, further comprising moving the crystal growth enclosure through the temperature gradient while depositing the Al and N₂ vapor.

4. The method of claim 3, wherein the crystal growth enclosure is moved through the temperature gradient at a rate of approximately 0.5 mm/h to approximately 3 mm/h.

5. The method of claim 1, wherein substantially no Al vapor diffuses from the crystal growth enclosure while depositing the Al and N₂ vapor.

6. The method of claim 1, wherein the nucleation site is seeded.

7. The method of claim 1, wherein providing the Al and N₂ vapor comprises subliming solid source material.

8. The method of claim 7, wherein the solid source material comprises polycrystalline AlN.

9. The method of claim 1, wherein providing the Al and N₂ vapor comprises vaporizing Al and N₂ from solid AlN.

10. The method of claim 1, wherein providing the Al and N₂ vapor comprises injecting a source gas.

11. The method of claim 1, wherein the selective barrier comprises a bore extending through a wall of the crystal growth enclosure.

12. The method of claim 1, wherein the selective barrier comprises a seal disposed in the crystal growth enclosure, the seal configured to substantially prevent passage of vapor therethrough when vapor pressures interior and exterior to the crystal growth enclosure are at mechanical equilibrium, and to permit passage of vapor therethrough when the vapor pressures are not at mechanical equilibrium.

13. The method of claim 1, wherein maintaining the N₂ partial pressure greater than stoichiometric pressure relative to the Al comprises maintaining the N₂ partial pressure at greater than two times the stoichiometric pressure relative to the Al.

14. The method of claim 1, further comprising providing hydrogen in the crystal growth enclosure, the hydrogen constituting up to approximately 5% of a vapor mixture comprising the hydrogen and the Al and N₂ vapor.

15. The method of claim 1, wherein a diffusion length of Al transport is less than 2 cm.

16. The method of claim 2, wherein the temperature gradient is formed at least in part by the arrangement of metallic baffles outside of the crystal growth enclosure.

17. The method of claim 16, wherein (i) a first set of metallic baffles is disposed at a proximal end of the crystal growth enclosure, (ii) a second set of metallic baffles is disposed at a distal end of the crystal growth enclosure, and (iii) a number of metallic baffles in the first set is different from a number of metallic baffles in the second set.

18. The method of claim 16, wherein at least one of the metallic baffles defines a hole therethrough.

19. The method of claim 2, wherein the thermal gradient is greater than 100°

/cm.

20. The method of claim 2, wherein the thermal gradient is an axial thermal gradient.

21. The method of claim 1, wherein depositing the Al and N₂ vapor forms a bulk AlN single crystal, and further comprising slicing or cutting the bulk AlN single crystal to form a single-crystal AlN substrate.

22. The method of claim 21, further comprising removing surface damage from a surface of the single-crystal AlN substrate.

23. The method of claim 21, further comprising depositing an epitaxial layer on a surface of the single-crystal AlN substrate.

24. The method of claim 23, wherein the epitaxial layer comprises Al_xGa_yIn_1-x-yN, wherein 0≦

x≦

1 and 0≦

y≦

1-x.